In physics, bottomness (symbol B′; using a prime as plain B is used already for baryon number) or beauty is a flavour quantum number reflecting the difference between the number of bottom antiquarks (n) and the number of bottom quarks (n) that are present in a particle:
B\prime=-(nb-n\bar)
Bottom quarks have (by convention) a bottomness of -1 while bottom antiquarks have a bottomness of +1. The convention is that the flavour quantum number sign for the quark is the same as the sign of the electric charge (symbol Q) of that quark (in this case, Q = -).
As with other flavour-related quantum numbers, bottomness is preserved under strong and electromagnetic interactions, but not under weak interactions. For first-order weak reactions, it holds that
\DeltaB\prime=\plusmn1
This term is rarely used. Most physicists simply refer to "the number of bottom quarks" and "the number of bottom antiquarks".